Sunscreens Can Attack Skin Cells

Led by Kerry M. Hanson, a senior research scientist in the Department of Chemistry at the University of California Riverside (UCR), the researchers report that three ultraviolet radiation (UV) filters (octylmethoxycinnamate, benzophenone-3 and octocrylene), generate reactive oxygen species (ROS) in skin themselves when exposed to ultraviolet radiation, thus augmenting the ROS that is naturally produced. These filters are approved by the Food and Drug Administration and widely used in sunscreens. The researchers note that the additional ROS are generated only when the UV filters have penetrated into the skin and, at the same time, sunscreen has not been reapplied to prevent ultraviolet radiation from reaching these filters.

"Sunscreens do an excellent job protecting against sunburn when used correctly," said Hanson, who works in the laboratory of Christopher Bardeen, an assistant professor of chemistry at UCR. "This means using a sunscreen with a high sun protection factor and applying it uniformly on the skin. Our data show, however, that if coverage at the skin surface is low, the UV filters in sunscreens that have penetrated into the epidermis can potentially do more harm than good.”

In their research, Hanson and colleagues used epidermal model tissue and applied sunscreen to the surface to test the effect of sunscreen penetration on ROS levels in the deep epidermis. A two-photon fluorescence microscope allowed them to visualize ROS generation occurring below the skin surface. The ROS activity was detected using a probe molecule whose fluorescent properties change upon exposure to ROS. On comparing images taken before and after the skin was exposed to UV radiation, they found that ROS generation in the skin increased after sunscreen penetration.